Crude oil produced from subterranean wells is frequently contaminated with undesirable materials. The most common of these materials is water. The fluid produced from an oil well can contain anywhere from less than 1% water to 99% water or more. Produced fluids containing these high "water cuts" are treated to remove most or all of the water because crude oil sales contracts typically allow a maximum of 1 to 3% water.
After treatment, the crude oil stream is monitored to determine the amount of water remaining in the crude. Various methods of monitoring the water content of a crude oil stream have been proposed. For example, U.S. Pat. No. 4,596,136 describes a system in which a sample of oil is removed. This system (and all others which require the removal of a sample) assume that the water content of the sample is representative of the water content of the entire flow stream. This is frequently not a valid assumption, particularly in large pipelines which contain significant concentrations of water.
Other methods have also been proposed. For example, spinners, venturies, or capacitance probes have been used to determine the water content of crude oil. Among other disadvantages, all of these systems require the insertion of one or more devices into the crude oil stream. These intrusive systems can significantly increase the pressure drop in a pipeline, requiring additional pumping capacity. Many of these devices also assume that the conditions in one portion of the pipeline are representative of the entire pipeline. This again may not be the case.
In summary, there is a need to provide a method and means for determining the water content of flowing crude oil streams which is highly accurate, nonintrusive, and which does not require the removal of a sample that is representative of the entire crude oil stream.